Fishery, systematics and stock dynamics of billfishes landed along the Indian coast

Stock dynamics of billfishes

Abstract

Sailfishes, marlins, spearfishes and swordfishes commonly referred to as billfishes are highly
migratory species, with a worldwide distribution in tropical and subtropical oceans. The
landings of billfishes along the Indian coast registered an increasing trend with an estimated
landing of 14,759 t in 2019. Kerala (41%) contributed the maximum followed by Tamil Nadu
(28%), Andhra Pradesh (18%), Gujarat (8%) and Maharashtra (2%) to the total billfish landings
during the last decade. Mechanised gillnetter cum hook and line was the major gear landing
billfishes. The major species landed during 2012-2019 were Istiophorus platypterus (52.2%),
Istiompax indica (21.1%), Makaira nigricans (7.3%), Xiphias gladius (17.2%) and Kajikia audax
(2.3%). Four of these species could be easily distinguished by COI barcodes but, the striped
marlin, K. audax showed high sequence similarity with K. albida and cannot be distinguished
by barcodes alone. Control region (889 bp) provided a better phylogenetic signal, consistent
with that of the whole mitochondrial genome topology. The stock status plots of billfishes
depicted that, all the species were in the developing and exploited phase. Growth, mortality
and exploitation rates estimated for four billfishes indicated that the present fishing rates
and biomass levels are at safe levels and there is considerable scope for enhancing their
fishery.

Keywords:
CO1 barcodes, Exploitation rate, Large pelagics,
Life history, Stock status plots